The present invention relates to a method of producing a passive optical device including one or a plurality of reflection gratings, e.g. echelette gratings and at least one port for polychromatic light and a plurality of ports for monochromatic light.
Such a device employing a planar reflection grating is illustrated and described in an article by J. P. Laude and J. M. Lerner in SPIE, Vol. 503, Application, Theory and Fabrication of Periodic Structures (1984), entitled "Wavelength Division Multiplexing/Demultiplexing (WDM) Using Diffraction Gratings," at pages 22-28. FIG. 4a at page 24 of that publication shows a Stimax arrangement including a concave mirror for focusing. An array of light conductive fibers is positioned in front of a photolithographically produced slit in the center of a planar reflection grating (echelette grating). The diverging beam coming from one of the input fibers is reflected by the concave mirror in a parallel beam towards the reflection grating. The grating sends the light back angularly dispersed towards the mirror. The mirror then focuses the spectrally divided image of the input fiber onto the output fibers located in the center of the grating.
H. W. Yen et al in Optics Letters. Volume 6, No. 12, December 1981, pages 639-641, describe a planar Rowland spectrometer for fiber optic wavelength demultiplexing. FIG. 1 at page 639 of that publication is a schematic representation of a planar Rowland spectrometer composed of a planar waveguide covered on both sides and having two opposing curved frontal faces. Glass fibers are connected to one of the frontal faces. A flexible reflection grating is pressed onto the other frontal face.
Both of the above described components perform the function of a wavelength demultiplexer and wavelength multiplexer, respectively, in optical communications transmission systems.
The manufacture of such components is relatively complicated and expensive since the components, particularly the reflection gratings, must be produced in separate manufacturing processes and must then be aligned and mounted with great care.